Attack of the poisoned lettuces! The dangers lurking in pre-packaged salad leaves
21:00 GMT, 18 August 2012
It is there on every packet of salad: ‘wash before eating’. But how many of us will simply rip open the wrapping and empty the contents into a salad bowl, or tear it into a sandwich without a second thought
Doing so could yield unpleasant results, says the Food Standards Agency (FSA), the Government’s advisory body.
Last year, Spanish cucumbers and German beansprouts made headlines worldwide as being possible sources of a deadly outbreak. A variety of the bacterium E.coli that was pathogenic (capable of causing infection) had killed six people and left almost 300 very ill in Germany.
The lettuce we buy in the supermarket is a dead plant, say food safety experts
Most of us are aware of the risk of food poisoning from meat and poultry if they’re not properly stored, handled or cooked, but we don’t tend to think of vegetables and fruit as posing a risk to our health.
FSA chief scientist Andrew Wadge says: ‘Recent E.coli outbreaks linked with vegetables have shown that handling fresh produce can also spread harmful bacteria.’
Yet the FSA’s research revealed public complacency. ‘Perceived risk of food poisoning from vegetables was low, whereas most people questioned were cautious when handling meat,’ Wadge says.
But really, how much danger can lettuce pose And besides, doesn’t a bit of dirt do us good
To find out, The Mail on Sunday conducted a special investigation – and discovered food-poisoning bacteria could be present in one in 20 lettuces in some supermarkets.
We bought 120 whole lettuces, all British-grown, including little gem, round and cos, purchasing 20 from each of six different supermarkets: Waitrose, Marks & Spencer, Tesco, Sainsbury’s, Morrisons and Asda.
All the lettuces were taken to a food-testing laboratory and screened for Listeria monocytogenes and E.coli: both are strains of bacteria that can cause food poisoning if eaten.
Both strains are often present in agricultural settings, though the risk of contamination is minimal due to strict hygiene standards enforced on growers by the Department for Environment, Food and Rural Affairs.
‘Bacteria are all around us in the environment,’ says Bob Martin, a microbiologist and food safety expert at the FSA. ‘E.coli contamination is normally associated with animal or human faeces, which could be present in soil where crops are grown or in water used to irrigate them. It can also result from poor personal hygiene among agricultural workers.’
Listeria, an unavoidable environmental organism, lives on many plants, feeding on dead plant tissue.
‘The lettuce we buy in the supermarket is a dead plant,’ says Christine Dodd, professor of food microbiology at the University of Nottingham. ‘If it contains listeria colonies, the longer you keep it, the more they’ll grow, even in the fridge and irrespective of the use-by date. So it’s best to buy vegetables with the longest shelf life and not to keep them for days before eating.’
In our test, a reading of ten or less colony-forming units per gram (cfu/g) indicated a negative test for E.coli. According to the Institute of Food Science and Technology, the target level for E.coli in fresh veg is less than 100 cfu/g, with a maximum of 1,000 cfu/g. The Health Protection Agency says below 20 cfu/g in items sold as ready to eat is ‘satisfactory’; up to 100 cfu/g is ‘acceptable’.
Of the 120 lettuces we tested, three were contaminated: 2.5 per cent, or one in 40. A Morrisons lettuce contained 20 cfu/g, while one from Waitrose contained 490 cfu/g. ‘The higher level here could cause sickness or an upset stomach in some people,’ says Phil Wheat, chief executive of the Society for Applied Microbiology.
‘The very young, pregnant women and those with compromised immune systems, such as people having chemotherapy, would be more likely to get an upset stomach in this case.’
Of the high E.coli reading, a Waitrose spokesperson comments: ‘While we strictly enforce the highest hygiene standards at all farms supplying us, we would always recommend people follow Government advice and wash all produce.’
A spokesman for Morrisons said: ‘There’s nothing here to be concerned about but we recommend all customers follow the FSA’s recommendation that all lettuce be washed.’
Listeria was not present in any of the samples.
Today, iceberg lettuces are often grown in soil-free environments. However, this is no protection against contamination. According to Phil Wheat, the risk is from water used for irrigation, not soil. But he adds: ‘Handlers still need to practise scrupulous personal hygiene.’
Thankfully, outbreaks of harmful strains of E.coli are rare, but the FSA says it’s essential to thoroughly wash fruit and veg before eating them to protect against any nasties.
‘When buying salad veg, you won’t be able to see bacteria, but if a lettuce contains soil it’s more likely to contain organisms so it needs a really good wash,’ says Bob Martin. ‘Most produce in the shops is deceptive because it looks clean. But unless it’s labelled “washed and ready to eat” it must always be thoroughly washed.’
The message is clear: the risks may be small, but buy the freshest produce you can and, when firing up the summer barbecue, be just as careful preparing salads as when handling and cooking raw meat.